memcmp(3) [plan9 man page]
MEMCMP(3) Linux Programmer's Manual MEMCMP(3) NAME
memcmp - compare memory areas SYNOPSIS
#include <string.h> int memcmp(const void *s1, const void *s2, size_t n); DESCRIPTION
The memcmp() function compares the first n bytes (each interpreted as unsigned char) of the memory areas s1 and s2. RETURN VALUE
The memcmp() function returns an integer less than, equal to, or greater than zero if the first n bytes of s1 is found, respectively, to be less than, to match, or be greater than the first n bytes of s2. For a nonzero return value, the sign is determined by the sign of the difference between the first pair of bytes (interpreted as unsigned char) that differ in s1 and s2. If n is zero, the return value is zero. ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). +----------+---------------+---------+ |Interface | Attribute | Value | +----------+---------------+---------+ |memcmp() | Thread safety | MT-Safe | +----------+---------------+---------+ CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD. NOTES
Do not use memcmp() to compare security critical data, such as cryptographic secrets, because the required CPU time depends on the number of equal bytes. Instead, a function that performs comparisons in constant time is required. Some operating systems provide such a func- tion (e.g., NetBSD's consttime_memequal()), but no such function is specified in POSIX. On Linux, it may be necessary to implement such a function oneself. SEE ALSO
bcmp(3), bstring(3), strcasecmp(3), strcmp(3), strcoll(3), strncasecmp(3), strncmp(3), wmemcmp(3) COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. 2017-09-15 MEMCMP(3)
Check Out this Related Man Page
MEMCMP(3P) POSIX Programmer's Manual MEMCMP(3P) PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond- ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. NAME
memcmp - compare bytes in memory SYNOPSIS
#include <string.h> int memcmp(const void *s1, const void *s2, size_t n); DESCRIPTION
The memcmp() function shall compare the first n bytes (each interpreted as unsigned char) of the object pointed to by s1 to the first n bytes of the object pointed to by s2. The sign of a non-zero return value shall be determined by the sign of the difference between the values of the first pair of bytes (both interpreted as type unsigned char) that differ in the objects being compared. RETURN VALUE
The memcmp() function shall return an integer greater than, equal to, or less than 0, if the object pointed to by s1 is greater than, equal to, or less than the object pointed to by s2, respectively. ERRORS
No errors are defined. The following sections are informative. EXAMPLES
None. APPLICATION USAGE
None. RATIONALE
None. FUTURE DIRECTIONS
None. SEE ALSO
The Base Definitions volume of IEEE Std 1003.1-2001, <string.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html . IEEE
/The Open Group 2003 MEMCMP(3P)